Effects Of Side Radicals And Nonlinear Electron-lattice Interactions On Polarons

Based on the one-dimensional tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we studied the effects of side radicals,impurities and nonlinear electron-lattice interactions on polarons in the polymers:1. There just has the linear interaction of the electron-lattice in SSH model, which depends on the change of the bond length. But the elastic potential energy of the lattice depends on the square order of the bond length. Considering the second order of the electron-lattice interaction and the lattice potential on the same magnitude, it is necessary to study the second order of the electron-lattice interaction. Considering the second orderβon the SSH mode, we have studied the static and dynamic properties of polaron in the polymer. Results show: For static properties, as the second orderβenhances the electron-lattice coupling, the dimerization and the energy gap of the polymer have increased, but the bandwidth almost unchanged. For dynamic properties, the movement of the polaron is significantly impacted byβ. Withβincreasing, the velocity of polaron decreases, and the dissociation electric field of the polaron grows gradually. These phenomena indicate that the second orderβenhances the electron-lattice coupling.2. We studied the dynamic properties of the polaron in the polymer that containing the number of impurities and/or side radicals:(1)The speeds of electron and/or hole polaron are subject to different effects by impurities. When the electron and/or hole polaron have crossed the impurity region, the velocity will change. For the positive impurity potential, the velocity of electron polaron will reduce firstly and then increase, but the hole polaron increases firstly and then reduces. The velocities of electron and hole polaron are both impacted by the number of impurities, when the number of impurity ions is small, there is the little effect on the polaron velocity, but when the number of impurities continues to grow, the average velocity of electron and hole polaron begin to decrease. The potential intensity of impurities also affects the polaron velocity, when impurity potential is larger, the polarons are more difficult to cross the impurity region, and the average speed is also getting smaller and smaller. When the impurity potential increased to a certain degree, the polaron can no longer cross the impurity region, just oscillate in the impurity region.(2) For the dynamics of the polaron in polymers with side radicals: The electron polaron and the hole polaron velocities change differently when they cross the side radical region. For the positive potential of the side radicals, if the electron spin on the side radical is the same with the electron on the local energy of the electron (hole) polaron. The velocity of electron polaron is almost no change but the hole polaron velocity decreases with the number of the side radicals increasing. If we give the negative potential, the case will be reverse. If the electron spin on the side radical is different with the electron on the local energy of the electron (hole) polaron, the electron polaron and hole polaron are impacted by the potential in both cases. In addition, the polaron is effected by the hopping integral of the side radical: With the hopping integral increases, the average speed of electron polaron decreases continuously, the average speed of hole polaron increases.3. We study the lattice distortion induced by the side-radical is depinning by the external electric field:(1) As the hopping integral and the potential energy interaction, there could be the lattice distortion in the main chain, there could form two localized energy levels. And the lattice distortion is impacted by the hopping integral, the localization of the distortion will be stronger as the hopping integral is greater.(2) The appropriate electric field could make the lattice distortion in the chain be divorced from binding of the side radicals and move in an certain speed, the greater the hopping integral is, the greater the electric field is required. For a certain hopping integral and the potential energy, when the electric field increases to a certain extent, the distortion will be disintegrated.